Risk factors for thyroid optic neuropathy include smoking, radioactive iodine treatment

May 15, 1999

---Disc edema in a patient with thyroid optic neuropathy and field defect.

WAIKOLOA, Hawaii — Smoking and radioactive iodine treatment alone are two risk factors for developing thyroid optic neuropathy among patients with Graves’ hyperthyroidism.

“We now know that smoking is a significant risk factor,” said Robert L. Lesser, MD, a neuro-ophthalmologist in private group practice in Waterbury, Conn. “This is another reason to warn these patients that they should not be smoking. In fact, patients who have thyroid disease in general are seven times more likely to develop a more severe form of ophthalmopathy if they smoke.”

Combined treatment may be better

---Clinical photograph of a patient with marked limitation of gaze with thyroid optic neuropathy and minimal proptosis.

Radioactive iodine treatment alone also increases the risk of contracting or worsening ophthalmopathy. One study published last year showed that 15% of patients who were treated only with radioiodine developed or had worsening ophthalmopathy. In contrast, none of the patients who were treated with both radioiodine and prednisone had progression, and two-thirds showed improvement. Further, only 3% of those treated with methimazole had any worsening of eye disease.

“Presumably what happens with thyroid ophthalmopathy is that the lymphocytes that are targeting against the thyroid also react to the eye muscles. You end up with lymphocytic infiltration and mucin deposition,” said Dr. Lesser, who spoke here at Hawaii ‘99, sponsored by Ocular Surgery News and the New England Eye Center.

The inferior rectus, medial rectus and superior rectus are the most commonly involved muscles, “so it is really an eyeball diagnosis,” said Dr. Lesser, who recommends “a computerized tomography [CT] scan or magnetic resonance imaging [MRI] of the orbit with fat suppression to document enlargement of the muscles.”

Dr. Lesser cited a female patient with white eyes. “That doesn’t necessarily make a difference, though. Sometimes the eyes are congested and sometimes they are not,” he said. However, the patient also had minimal proptosis. “That is one of the tip-offs that there is a greater risk for thyroid optic neuropathy, be cause of the simple mechanical crowding phenomenon.”

Although the risk of developing the disease is relatively low (1% to 5%), vision loss is possible; therefore, these patients should be tested and followed closely. Moreover, the absence of disk edema does not exclude the diagnosis.

Test useful for early detection

---A CT and MRI of a patient with enlarged muscles secondary to thyroid optic neuropathy.

Visual-field and color-vision testing help in early detection. “Patients need to be alerted about the possibility of a change in vision and need to arrange to see you if this happens,” Dr. Lesser said. Low-dose radiation may be appropriate for even some of the congestive findings.

Once the diagnosis is made, Dr. Lesser starts patients on short-term steroids. “I do not favor using steroids on a long-term basis because I think the treatment becomes worse than the disease,” he said. He also mentioned that high-dose steroids may be appropriate in certain situations. “We are now becoming comfortable with 1 g of methylprednisolone intravenous for 3 to 5 days and seeing if that rapidly decompresses the muscle.”

Dr. Lesser’s patients are maintained on steroids throughout radiation treatment. “It is at that point that I taper the steroids and then measure the effect,” he said. “Results are quite good in most cases.” Surgical decompression of the orbit is reserved for those patients with a contraindication or intolerance. “You have several choices with decompression, including lateral wall, medial wall and inferior wall,” he said.

Overall, patients are “psychologically devastated” by thyroid orbitopathy, Dr. Lesser said. “A lot of these patients need counseling and support.”

For Your Information:

• Robert L. Lesser, MD, can be reached at 1201 W. Main St., Waterbury, CT 06708; (203) 597-9100; fax: (203) 597-1696. Dr. Lesser has no direct financial interest in any of the products mentioned in this article, nor is he a paid consultant for any companies mentioned.

Reference:

• Bartalena L, Marcocci C, Bogazzi F, et al. Relation between therapy for hyperthyroidism and the course of Graves’ ophthalmopathy. N Engl J Med. 1998;338(2):73-78.

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